Newfound exoplanet Kepler-62f is imagined in an illustration. The shining star to the right is Kepler-62e.

Marc Kaufmanfor National Geographic NewsPublished April 18, 2013

Planet hunters are significantly closer to their goal of finding an "Earth twin" with the discovery of two planets similar in size to our own, astronomers with NASA's Kepler mission announced today.

The planets, described at a NASA press conference, orbit a sun that's cooler than ours but is at the right distance to allow water to remain liquid, which is considered essential for a planet to support life. (Read about a related discovery in 2011: "NASA's Kepler Finds Two Earth-Size Planets Around Sunlike Star.")

And because of their sizes and orbits, the newfound planets are likely either rocky—like Earth—or watery, NASA scientists said. The two planets are located 1,200 light-years away in a five-planet system orbiting a star dubbed Kepler-62.

Called Kepler-62e and -62f, the planets "are by far the best candidates for habitability of any found so far," said William Borucki of NASA's Ames Research Center, the science principal investigator for the agency's Kepler Space Telescope.

In 1100 years they can point their radio antennas at us and pick up our "Hello universe!" signals. Too bad it'll be old radio broadcasts of Fibber McGee, and WW1 coverage, and Amos-n-Andy, and all that sort of stuff. May convince 'em to come stamp us out..

So far Kepler scientists have identified 350 Earth-size exoplanets. The two planets introduced today—called "super Earths"—are 1.4 and 1.6 times larger than Earth, and orbit around their sun in 122 and 267 days, respectively.

I'm not sure they can accurately compute the 'radius' (do you mean diameter?) of the planets. Mass is easier to measure and compute IIRC. Actual size is often by inference from mass and orbital mechanics.

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